Portable or hand-held power saws used for cutting masonry surfaces, pavements, and the like, have been known for some time. Examples of various types of power saws are described in Pat. Nos. 4,188,935, 3,896,783 and 3,656,468. Referring to prior art FIG. 1, there is shown a typical portable or hand-held power saw 10.
The typical portable power caw 10 includes an engine or motor 12 coupled to a saw body 14. Prior art FIG. 1 shows a gasoline powered engine 12, although other types of engines or motors can be used, such as a hydraulically or electrically powered motors. The engine 12 is operatively connected to a circular cutting tool such as a saw blade 16 arranged on an opposite end of the saw body 14. A blade guard 18 encloses a portion of the blade 16 and is connected to the saw body
The portable power saw 10 includes two handles 20 and These handles 20 and 22 can be arranged on either side of the engine 12 so as to provide the operator with a stable hold on the power saw 10. A power switch 24 is operatively arranged on the handle 20 for switching the power saw 10 on and off. In use, the operator typically grips the handle 20 with one hand and the handle 22 with his other hand. The operator's one hand can then operate the power switch 24 while the other hand can control the engagement of the saw blade 16 with the surface 28 to be cut.
Typical portable power saws weigh on the order of 20 to 40 lbs. In use therefore, this weight strains the operator. The operator must not only physically lift the power saw in order to locate the saw blade in the proper position for a cut, but he also typically must hunch forward in order to maintain engagement between the saw blade 16 and the cutting surface during the length of the cut. Extended use of a portable power saw thus quickly exhausts an operator's strength and places a strain on his back and arms. When using a portable power saw, it is advantageous to be able to precisely control the depth of a cut because the saw blades wear down and are expensive to constantly replace, cutting a surface at a greater depth than is necessary is disadvantageous as it results in excessive wear on the blade, as well as a slower cutting process than is optimal. However, it is often difficult for the operator of the portable power saw to cut at a constant depth throughout the extent of the cut. Many times, the operator simply cuts along the entire exposed portion of the saw blade 16 in order to assure himself that a sufficient cut was made.
In order to relieve the strain on the operator, as well as to help maintain a constant cutting depth, it has been heretofore known to make use of a pair of wheels 26 mounted on the blade guard 18. These wheels 26 provide a pivot axis for moving the power saw 10 between an at rest position as shown in prior art FIG. 1 and an operational position wherein the saw blade 16 is engaged into the cutting surface 28. The use of such wheels 26, however, does not fully relieve the strain on an operator using the portable power saw 10 as he still must stoop down to perform his cut, as well as lift the saw to engage a cut.
As an alternative, commercially available saw carts have been developed. A saw cart provides a frame to which the power saw can be mounted. The saw cart includes a set of wheels arranged behind the saw blade to provide a pivot axis much like the wheel set 26 shown in prior art FIG. 1. The saw cart further includes an extended cart handle which generally allows the operator to walk upright while pushing the cart along the length of the cut. However, use of a saw cart requires a time consuming mounting process for the power saw. The assembly or mounting time, as well as the disassembly time, is particularly disadvantageous when the power saw is frequently changed between its mounted saw cart and its hand-held state. Further, when the power saw is used with the saw cart, the weight of the entire assembly greatly increases.
While use of a wheel set or saw cart helps relieve some of the operator strain, numerous disadvantages arise with respect to the cutting process. While the wheel set or the wheels of the saw cart provide an adequate guide for performing straight cuts, it is extremely difficult to perform radius or curved cuts using these devices. This is due to the fact that the pivoting axis of the wheel set is positioned behind the arbor of the saw blade, i.e., the axis of rotation of the saw blade. When a radius or curved cut is attempted, the wheels must be skidded or slid transverse to their rolling direction in order to allow the saw blade 16 to make a radius cut. The friction generated by the wheels inhibits the turning ability of the power saw and causes increased contact between the side faces of the saw blade 16 and the groove being cut. This results in a strain on the blade side face as well as excessive wear and damage to the blade. Further, the strain on the operator is increased as he attempts to skid the wheels so as to make a radius cut.
Another disadvantage with the use of the prior known wheel sets and saw carts is that the depth of the out can substantially vary due to any pivoting motion about the awls of the wheels. Because the pivot axis of the wheels, and hence the power saw, is substantially offset from the cutting point of the saw blade, i.e., the portion of the saw blade 16 which engages the cutting surface 28, even the slightest variation in the pivot angle about the wheels causes an amplified variation of the depth of the cut. In field use, this results in uneven cuts being generated along the length of the cut due to an operator's slight variation of the pivot angle of the power saw.
There is therefore needed a guide for a portable power saw which overcomes the above-mentioned problems associated with the prior art.